Hitherto, in a polymerization reaction of an olefin-based polymer, a polymerization catalyst containing, for example, a transition metal compound and a promoter component (e.g., a metallocene catalyst or a Ziegler catalyst) has been generally used. In such polymerization reaction, it is preferred from an economical point of view that activity be improved. In addition, the activity improvement is preferred also from the viewpoint that an amount of a catalyst residue to be contained in a product polymer can be reduced to improve product quality. Therefore, various technological developments concerning the polymerization reaction of the olefin-based polymer have heretofore been made for the purpose of the activity improvement.
An example of the technological developments is specifying of the transition metal compound or the promoter component. In addition to that, reaction conditions have also been investigated in detail. As a result, it has heretofore been found that compounds such as water, carbon monoxide, carbon dioxide, and carbonyl sulfide are catalyst poisons for the polymerization catalyst. Particularly in polymerization involving using a metallocene catalyst having high activity, an amount of the catalyst to be used is small, and hence the catalyst poisons have large influences on the polymerization reaction. On the basis of this finding, various production methods have been developed. For example, there is known a method involving purifying a solvent, a monomer, or the like, to thereby reduce amounts of those compounds to certain amounts or less, and then performing the reaction. As specific means therefor, in Patent Literature 1, there are disclosed methods to be performed before the polymerization reaction, for an impurity contained in the solvent or the monomer to be used, as follows: a method involving allowing an inert gas, such as nitrogen or argon, to flow through the solvent or the monomer; a method involving loading sodium or potassium metal and then performing distillation in an inert gas atmosphere; and a purification method involving using an adsorbent, such as nickel, zinc oxide, copper sulfide, silica, or activated carbon. In addition to that, there is known a method involving adding a scavenger in order to neutralize the poisons of the above-mentioned compounds remaining in a reaction system. For example, in Patent Literature 2, an organoaluminum compound is disclosed as the scavenger.